1. Field of the Invention
The present invention relates to an uncooled infrared (IR) imaging apparatus, and more particularly, to a bipolar junction transistor (BJT)-based uncooled IR sensor capable of being implemented through a complementary metal oxide semiconductor (CMOS) compatible process and improving temperature change detection characteristics.
2. Description of the Related Art
Recently, uncooled IR sensors has been actively researched and developed in terms of advantages such as a low production cost, a light weight, a low operating voltage, and a wide IR frequency band, etc. The applications of the uncooled IR sensors have been widened into a night IR imaging apparatus for a vehicle, an IR scope for a game machine, a security camera, thermal analysis, fire detection, and the like.
Particularly, in case of a CMOS process compatible IR sensor, since peripheral circuits such as a read-out integrated circuit (ROIC) can be formed on the same substrate for the IR sensor, a monolithic IR detection system can be implemented.
Therefore, a production cost can be greatly reduced, and operating characteristics such as noise reduction and an increase in signal processing speed can be improved.
On the other hand, various technologies for forming micro-bolometers on a substrate where the CMOS ICs are formed by using a surface micro-machining process to implement the uncooled IR sensor have been proposed.
In general, the micro-bolometers have a structure where the micro-bolometers are formed to be floated apart from the substrate in order to remove thermal noise caused from heat of the substrate. In addition, the micro-bolometers are constructed with heat absorption layers which absorb the heat and heat detection devices which detect a change in heat and change resistance thereof with a high temperature coefficient of resistance (TCR).
As an example of a heat detection device having a high TCR, there are VOx, polycrystalline SiGe, amorphous silicon, YBaCuO, and various metallic resistors, etc.
However, the VOx is not compatible with a CMOS process, but many additional processes as well as the CMOS process are needed. Accordingly, apparatuses for depositing the VOx and post-processing apparatus after the deposition of VOx are additionally needed, so that the production cost is increased.
In addition, due to an amorphous structure of the VOx, a low frequency noise is increased.
On the other hand, the polycrystalline SiGe or the amorphous silicon is compatible with the CMOS process. However, since a high-temperature heat treatment process for ensuring stability of resistor is additionally needed, the polycrystalline SiGe or the amorphous silicon cannot be integrated into a CMOS IC in a monolithic type. In addition, due to an amorphous characteristic, a low frequency noise is increased. In addition, many additional processes such as thin film deposition, photolithography, and etching are needed.
In order to solve the aforementioned problems, a technology for implementing the heat detection device of the micro-bolometers by using PN diodes shown in FIG. 1 has been proposed.
According to some research, in temperature change detection characteristics of the uncooled IR sensor implemented by using the PN diode as the heat detection device, a rate of change in voltage according to a temperature is in a range of 1 to 3 mV/K. The value is much more excellent than the value of a silicon thermocouple, that is, in a range of 0.5 to 1 mV/K.
In addition, the PN diode sensor is compatible with a silicon CMOS process, and a minimum of additional process after the CMOS process is needed.